Hi all,

I've got a whole stack of circuit breakers from work and was wondering if anyone has had any experience with using these rather than a fuse box, and what the sva guy's say about them.

Cheers
chris

[Edited on 29/4/03 by flyingkiwi]

if they are not designed for 12 v systems they might have sluggish trip characteristics.

Id test them in your application - ie put a 10a load on a 5a breaker and see if it trips


atb

steve

Cheers steve, was just having a look at them and noticed they're 28v. bugger! Was wondering if you knew how to work out the correct fuse amp for a circuit. I'm guessing that if the circuit runs a steady say 3 amps (ie, the light's - but I'm just guessing) then there must be a max figure in which will pop the fuse, how do you work that out??

If I do whack a 10a current through a 5a circuit breaker, what response should I be looking at? Instantanious or some sort of delay. I'm imagining that without knowing the stat's of the breakers, this could be hard to work out!

Am I just talking a load of bollocks????

Chris

I might be adding to the bollox as although im an electronics design engineer im not an expert at mechanical circuit breakers.

Circuit breakers work by either a heating effect tripping the mechanicals or by a magnetic effect - both of which become greater with the higher load thats drawn.

Fuses and circuit breakers all have different chractersitics. You can get varieties that blow fast or slow. For example, motor control breakers in inductrial systems can be rated at 5 amps but take a 16 amp initial starting surge for a few milliseconds without flinching. Then there are types that will trip in that application.

Fuses and circuit breakers are not precision devices. I have seen rating tables for fuses that show a 20% overload can take an hour to blow the fuse, or for further illustration, take a second or two even at 100% overload.

A short however draws a massive curent so you typcally see a fuse blow instantaneously.

If I were you id look for a data sheet for the breakers - perhaps on the net. The 28v rating is probably a maximum contact switching, and you may find they are great at 12v.

Id expect your breaker to take a short while to trip even at 100% overload. Shorting it out will most likely trip it, but you might need something a little more finer as a test!

I used conventional fuses. They are also almost free. You can get the fuses from the donor, or any scrap car when next at the breakers - they fit in yer pocket and im sure the scrappy wont mind ;0).

A couple fuse boxes (I used two 8 way ones and still needed more) can be bought from europa or vehicle wiring products for 8 quid or so. Easy to mount and wire.


As far as rating is concerned, the original application fuse in the car or hanes manual for it is a good guide.

In general I would add about 20% to the normal running current.

Ohms law can help you to find current if you know the wattage and volts (use 13.8v for a car cos its at that level when alternator is spinning)

W
---- = I
V




atb


steve


[Edited on 30/4/03 by stephen_gusterson]

Cheers steve, you answered the questions I just found out a work! The circuit breakers were free, thanks to a wayward pilot and the ground, and are rated at 28v max. Have tested them and they pop fine running on 12v.

Wanted to use them rather than fuses, as they look cool and I never seem to have the fuse I need when the buggers blow!

Cheers
Chris

nice to know we got that one sorted!

atb

steve